Thickening agents for unsaturated polyester resin compositions

ABSTRACT

A thickening agent for unsaturated polyester resin compositions comprises 
     (a) 25% to 70% by weight of a Group II-A metal oxide or hydroxide and 
     (b) 30% to 75% by weight of an unsaturated polyester vehicle comprising 
     (1) 50% to 100% by weight of an unsaturated polyester that is the product of the reaction of a dicarboxylic acid component that contains at least one unsaturated aliphatic dicarboxylic acid and at least one saturated aromatic dicarboxylic acid with an alcohol component that contains at least one glycol and at least one monohydric alcohol and 
     (2) 0-50% by weight of an unsaturated monomer capable of reacting with the unsaturated polymer to form cross-linkages.

This invention relates to thickening agents for unsaturated polyesterresin compositions and to unsaturated polyester resin compositions thatcontain these thickening agents.

Polyester resin compositions that have been rendered insoluble andinfusible by cross-linking are commercially important types of polymericmaterials that are widely used in casting, laminating, filament winding,and other such applications in which the resin is cured in place. Thecross-linked polyester resin systems are used, for example, in themanufacture of fiber reinforced compositions in which glass or otherfibers are embedded in a matrix of the resin. The resulting sheetmolding compounds (SMC) and bulk molding compounds (BMC) are being usedwith increasing frequency in compression molding operations. SMCtechnology always employs chemical thickening of the resin matrix duringformulation, and BMC technology often employs this technique.

Chemical thickening involves the interaction of residual carboxyl and/orhydroxyl groups on the linear chains of the polyester resin withalkaline earth metal oxides and hydroxides to increase the viscosity ofthe uncrosslinked resin during maturation after compound preparation.Typical SMC molding viscosities range from 10-60,000,000 cps., dependingupon the application. The purpose of the chemical thickening agent is toprovide a tack-free SMC sheet stiff enough to permit easy handling andto provide sufficient resin viscosity to carry glass fibers to theextremities of the mold in a flow situation during crosslinking of thesystem. Low viscosity compounds can result in resin washing and poorcarry of reinforcing fibers, particularly in large molded parts.

The alkaline earth metal oxides and hydroxides that are used as chemicalthickeners can be added to the polyester resin compositions as drypowders or as dispersions in resinous vehicles. The use of dispersionsis generally preferred because they protect the thickener from moistureand carbon dioxide, they are non-dusting, and they are easy to handle.Thickener dispersions that have been widely used heretofore have beenmade by dispersing the alkaline earth metal oxide or hydroxide incurable polyesters that have acid numbers of about 20. Because thesepolyesters undergo a reaction with the metal oxides and hydroxides thatresults in the thickening of the dispersions, the amount of thethickener that can be used in the dispersions is limited to that whichwill produce a handleable dispersion. For example, a dispersion of 40%by weight of magnesium oxide in a conventional polyester resin isdifficult to handle because it has a putty-like consistency.

In accordance with this invention, it has been found that stable,non-thickening fluid dispersions that contain as much as 70% by weightof an alkaline earth metal oxide or hydroxide can be prepared bydispersing an alkaline earth metal oxide or hydroxide in a polyestervehicle that has a low viscosity, very low acid number, and excellentwetting properties. These dispersions, which can be poured, pumped, andmetered, can be readily and uniformly incorporated into SMC and BMCformulations.

The thickening agents of this invention are dispersions of oxides and/orhydroxides of metals of Group II-A of the Periodic Table of Elements instable, low-viscosity, curable polyester vehicles that compriseunsaturated polyesters prepared by the reaction of a dicarboxylic acidcomponent that contains an unsaturated aliphatic dicarboxylic acid and asaturated aromatic dicarboxylic acid and an alcohol component thatcontains a glycol and a monohydric alcohol and, optionally, unsaturatedmonomers that are capable of reacting with the unsaturated polyesters toform cross-linked polyester resins.

The unsaturated polyesters that are components of the curable polyestervehicles in which the chemical thickeners are dispersed are prepared bythe reaction of a dicarboxylic acid component with an alcohol componentin the amounts of 0.4 mole to 0.6 mole of the dicarboxylic acidcomponent per mole of the alcohol component. To be useful in thepreparation of these unsaturated polyesters, the dicarboxylic acidcomponent must contain from 80 to 90 mole percent of at least oneunsaturated dicarboxylic acid having 4 to 8 carbon atoms and 10 to 20mole percent of at least one saturated aromatic dicarboxylic acid,preferably 83 to 87 mole percent of an unsaturated aliphatic acid and 13to 17 mole percent of a saturated aromatic acid. Illustrative of theunsaturated aliphatic dicarboxylic acids that can be used in thepreparation of the unsaturated polyesters are maleic, fumaric,chloromaleic, ethylmaleic, dimethylmaleic, glutaconic, itaconic,mesaconic, citraconic, acetylenedicarboxylic acids, and mixturesthereof, as well as the anhydrides, acid halides, and lower alkyl estersof these acids. Suitable aromatic acids include phthalic, isophthalic,terephthalic, tetrachlorophthalic, tetrabromophthalic,dibromotetrahydrophthalic acids, and mixtures thereof, and thecorresponding anhydrides, acid halides, and lower alkyl esters. Thedicarboxylic acid component preferably contains fumaric acid andisophthalic acid.

The alcohol component that is used in the preparation of the unsaturatedpolyesters contains 40 to 60 mole percent of at least one glycol having2 to 6 carbon atoms and 40 to 60 mole percent of at least one monohydricalcohol having 6 to 10 carbon atoms, preferably equimolar amounts of themono- and dihydric alcohols. Examples of the useful glycols are ethyleneglycol, diethylene glycol, propylene glycol, dipropylene glycol,butanediol, hexanediol, neopentyl glycol, and dibromoneopentyl glycol.The monohydric alcohol may be, for example, n-hexanol,2-methylpentanol-1, 2-ethylbutanol-1, neopentyl carbinol, n-heptanol,n-octanol, 2-ethylhexanol, deconol, or dodecanol. The alcohol componentpreferably contains ethylene glycol and 2-ethylhexanol.

The unsaturated polyesters are prepared by the conventional procedure,that is, by reacting the dicarboxylic acid component with the alcoholcomponent at a temperature in the range of 130° C. to 220° C. in thepresence of an esterification catalyst, such as p-toluenesulfonic acidor benzenesulfonic acid, and in an atmosphere of inert gas, such asnitrogen or carbon dioxide, until the desired unsaturated polyester isobtained. This polyester usually has an acid value of 0.1 to 5,preferably 0.5 to 4, and a hydroxyl value of 100 to 160, preferably 125to 135.

While this unsaturated polyester can be used as the sole component ofthe polyester vehicle in which the thickener is dispersed, it ispreferably used in combination with an unsaturated monomer that iscapable of reacting with the polyester through its unsaturated acidcomponent to form cross-linkages. Suitable monomers include styrene,methylstyrene, dimethylstyrene, divinylbenzene, vinyltoluene,dichlorostyrene, methyl acrylate, ethyl acrylate, methyl methacrylate,diallyl phthalate, triallyl cyanurate, trimethylolpropane diallyl ether,neopentyl glycol diacrylate, vinyl acetate, acrylonitrile, acrylamide,and mixtures thereof. The relative amounts of the polyester and monomerin the polyester vehicle may be varied over a wide range. The vehicleusually contains from 5% to 50% by weight of the monomer, with themonomer content preferably in the range of 10% to 20% by weight.

The thickening agents of this invention contain from 25% to 70% byweight, usually 30% to 60% by weight, of a thickener that is an oxide orhydroxide of a metal of Group II-A of the Periodic Table of Elements inthe unsaturated polyester vehicle. Suitable thickeners include theoxides and hydroxides of magnesium, calcium, strontium, and barium. Forreasons of efficiency and economy, magnesium oxide, magnesium hydroxide,calcium oxide, calcium hydroxide, and mixtures thereof are the preferredthickeners.

The thickening agents are prepared by grinding a mixture that comprisesthe metal oxide or hydroxide and the unsaturated polyester vehicle in aball mill, sand mill, dispersion mill, colloid mill, or high shear mixeruntil a uniform dispersion is obtained. In addition to the thickener andvehicle, the dispersions may contain such additives as viscositymodifiers, for example, isopropyl triisostearoyl titanate, isopropyltrimethacryl titanate, and zinc naphthenate; and acid neutralizers, forexample, dimethylaminoethanol and other amines. The thickening agentsprepared in this way are characterized by low viscosity, excellentstability, and compatibility with all types of polyester resins.

The unsaturated polyester resin compositions into which the thickeningagents of this invention are incorporated include sheet moldingcompounds (SMC) and bulk molding compounds (BMC) that comprise anunsaturated polyester resin and an unsaturated monomer capable ofreacting with the polyester through its unsaturated acid component toform cross-linkages.

The unsaturated polyester resins that are used in the production ofthese molding compounds are formed by condensing a saturateddicarboxylic acid of anhydride and an unsaturated dicarboxylic acid oranhydride with a dihydric alcohol. Illustrative of these polyesterresins are the products of the reaction of a saturated dicarboxylic acidor anhydride, such as phthalic anhydride, isophthalic acid,tetrahydrophthalic anhydride, endomethylene tetrahydrophthalicanhydride, tetrachlorophthalic anhydride, hexachloroendomethylenetetrahydrophthalic acid, succinic acid, glutaric acid, adipic acid,pimelic acid, suberic acid, azelaic acid, and sebacic acid, and anunsaturated dicarboxylic acid or anhydride, such as maleic anhydride,fumaric acid, chloromaleic acid, itaconic acid, citraconic acid, andmesaconic acid, with a dihydric alcohol, such as ethylene glycol,propylene glycol, butylene glycol, diethylene glycol, triethyleneglycol, and neopentyl glycol. Small amounts of a polyhydric alcohol,such as glycerol, pentaerythritol, trimethylolpropane, or sorbitol, maybe used in combination with the glycol.

A three-dimensional structure is produced by reacting the unsaturatedpolyester with an unsaturated monomer, such as styrene, methylstyrene,dimethylstyrene, vinyltoluene, divinylbenzene, dichlorostyrene, methylacrylate, ethyl acrylate, methyl methacrylate, diallyl phthalate, vinylacetate, triallyl cyanurate, acrylonitrile, acrylamide, and mixturesthereof. The unsaturated polyester resin compositions generally contain20% to 80% by weight of the monomer, with the monomer content preferablyin the range of 30% to 70% by weight.

The amount of the thickening agent that is incorporated in theunsaturated polyester resin compositions is that which will result inthe formation of tack-free, high-viscosity molding compounds. In mostcases, the amount of the thickening agent used is that which willprovide from 0.5 part to 25 parts by weight, preferably 1 part to 5parts by weight, of the alkaline earth metal oxide or hydroxide per 100parts by weight of the unsaturated polyester resin composition.

In addition to the unsaturated polyester resin, cross-linking monomer,and thickening agent, the unsaturated polyester resin compositions ofthis invention may contain such conventional ingredients as free-radicalpolymerization catalysts, catalyst accelerators, inhibitors,stabilizers, plasticizers, flame-retardants, mold release agents,reinforcing fibers, inert fillers, pigments, and the like in the amountsordinarily used for these purposes.

The invention is further illustrated by the following examples. In theseexamples, all parts are parts by weight and all percentages arepercentages by weight.

EXAMPLE 1

A. A reaction mixture that contained 1.00 mole of ethylene glycol, 1.01mole of 2-ethylhexanol, 0.91 mole of fumaric acid, 0.15 mole ofisophthalic acid, and a catalytic amount of p-toluenesulfonic acid washeated at a temperature in the range of 130° to 220° C. in an atmosphereof nitrogen to form an unsaturated polyester that had an acid value of1.9, a hydroxyl value of 110, and a viscosity of 229 cps. Subsequently,86.3 parts of this unsaturated polyester was mixed with 13.7 parts oftrimethylolpropane diallyl ether to form an unsaturated polyestervehicle.

B. Two hundred parts of the unsaturated polyester vehicle was thoroughlymixed with 1 part of isopropyl triisostearoyl titanate (TTS Titanate).This mixture was agitated vigorously while 200 parts of magnesium oxide(Maglite A) was added to it. Agitation was continued until a uniform,lump-free dispersion was obtained. The viscosity of this 50% magnesiumoxide dispersion in the unsaturated polyester vehicle was as follows:

    ______________________________________                                        Brookfield Viscosity    Viscosity                                             ______________________________________                                        at 25° C. using #7 spindle at                                                                  (cps)                                                  2 rpm                  60,000                                                 4 rpm                  50,000                                                10 rpm                  50,000                                                20 rpm                  51,000                                                ______________________________________                                    

C. One hundred parts of a commercially-available, reactive polyesterresin (Hatco Polyester G-R 13031) was mixed thoroughly with 2 parts ofthe 50% MgO dispersion, and the mixture was placed in an oven at 70° C.After 6 hours at 70° C., a tack-free sheet was obtained.

EXAMPLE 2

A. Two hundred parts of the unsaturated polyester vehicle whosepreparation is described in Example 1A was agitated vigorously while 100parts of magnesium oxide (Maglite A) was added to it. The agitation wascontinued until a uniform, lump-free dispersion was obtained. Theviscosity of this 33% MgO dispersion in the unsaturated polyestervehicle was as follows:

    ______________________________________                                        Brookfield Viscosity    Viscosity                                             ______________________________________                                        at 25° C. using #4 spindle at                                                                  (cps)                                                  2 rpm                  1,000                                                  4 rpm                  1,000                                                 20 rpm                    900                                                 ______________________________________                                    

B. Two parts of the 33% MgO dispersion was mixed thoroughly into 100parts of a commercially-available reactive polyester resin (HatcoPolyester G-R 13031). The mixture was placed in an oven at 70° C. After6 hours' heating, a tack-free sheet was obtained.

EXAMPLE 3

A. An unsaturated polyester was prepared by the reaction of 1.00 mole of2-ethylhexanol, 1.15 mole of ethylene glycol, 0.89 mole of fumaric acid,and 0.15 mole of isophthalic acid. This polyester had an acid value of1.5 and a hydroxyl value of 115.

An unsaturated polyester vehicle was formed by mixing 85 parts of theunsaturated polyester with 15 parts of styrene.

B. A series of dispersions was prepared by thoroughly mixing 100 partsof the unsaturated polyester vehicle with varying amounts of eithermagnesium oxide (Maglite D) or magnesium hydroxide (Marinco H) andagitating the mixtures vigorously until uniform, lump-free, stabledispersions were obtained.

The following dispersions were prepared in this way:

1. 25% MgO in polyester vehicle

2. 30% MgO in polyester vehicle

3. 55% MgO in polyester vehicle

4. 25% Mg(OH)₂ in polyester vehicle

5. 40% Mg(OH)₂ in polyester vehicle

6. 50% Mg(OH)₂ in polyester vehicle

7. 60% Mg(OH)₂ in polyester vehicle

C. When 2 parts of each of these dispersions was mixed thoroughly with100 parts of a 30% styrenated polyester resin (U.S. Steel Corp.Polyester Resin USS MR 941) and the resulting mixture was heated at 70°C., a tack-free sheet was obtained in 8 hours or less.

The procedure described in Example 3 can also be used to producethickener dispersions that contain from 30% to 60% of calcium oxide,calcium hydroxide, strontium oxide, strontium hydroxide, barium oxide,barium hydroxide, or mixtures of each of these compounds with magnesiumoxide and/or magnesium hydroxide.

What is claimed is:
 1. A thickening agent for unsaturated polyesterresin compositions that comprises(a) 25% to 70% by weight of a thickenerthat is a Group II-A metal oxide or hydroxide and (b) 30% to 75% byweight of an unsaturated polyester vehicle comprising(1) 50% to 95% byweight of an unsaturated polyester that is the product of the reactionof a dicarboxylic acid component containing 80 to 90 mole % of at leastone unsaturated aliphatic dicarboxylic acid having 4 to 8 carbon atomsand 10 to 20 mole % of at least one saturated aromatic dicarboxylic acidwith an alcohol component containing 40 to 60 mole % of at least oneglycol having 2 to 6 carbon atoms and 40 to 60 mole % of at least onemonohydric alcohol having 6 to 12 carbon atoms, in the amount of 0.4mole to 0.6 mole of the dicarboxylic acid component per mole of thealcohol component, and (2) 5 to 50% by weight of an unsaturated monomercapable of reacting with said unsaturated polyester to formcross-linkages.
 2. A thickening agent for unsaturated polyester resincompositions as defined in claim 1 that contains 30% to 60% by weight ofthe thickener.
 3. A thickening agent for unsaturated polyester resincompositions as defined in claim 1 wherein the thickener is magnesiumoxide.
 4. A thickening agent for unsaturated polyester resincompositions as defined in claim 1 wherein the thickener is magnesiumhydroxide.
 5. A thickening agent for unsaturated polyester resincompositions as defined in claim 1 wherein the unsaturated polyestervehicle contains 80 to 90% by weight of said unsaturated polyester and10% to 20% by weight of said unsaturated monomer.
 6. A thickening agentfor unsaturated polyester resin compositions as defined in claim 1wherein the unsaturated polyester vehicle contains an unsaturatedpolyester that is the product of the reaction of a dicarboxylic acidcomponent containing 83 to 87 mole % of fumaric acid and 13 to 17 mole %of isophthalic acid with said alcohol component.
 7. A thickening agentfor unsaturated polyester resin compositions as defined in claim 1wherein the unsaturated polyester vehicle contains an unsaturatedpolyester that is the product of the reaction of said dicarboxylic acidcomponent with an alcohol component that contains equimolar amounts ofethylene glycol and 2-ethylhexanol.
 8. A thickening agent forunsaturated polyester resin compositions as defined in claim 1 whereinthe monomer in the unsaturated polyester vehicle is trimethylolpropanediallyl ether.